The present invention relates to a warm-up apparatus for a fuel evaporator. The fuel evaporator (also referred to as a fuel vaporizer) evaporates raw fuel liquid, such as a mixture of methanol and water, and supplies raw fuel gas to a reformer, in which the raw fuel liquid as a raw fuel gas is reformed to produce hydrogen and the produced hydrogen is supplied to a fuel cell.
In a conventional fuel cell system, warm-up apparatuses employing an electric heater 101 shown in FIG. 4A or a combustion burner 201 shown in FIG. 4B are widely known to immediately warm up a fuel evaporator 100 or 200 evaporating raw material to be supplied to a reformer. The raw material is then reformed at the reformer. The warm-up apparatus warms up the fuel evaporator either directly or indirectly. In the indirect heating, gas or liquid is heated by a heat source, such as the electric heater 101 or the combustion burner 201, and the heated gas or liquid is used as a heat transfer medium.
For example, Japanese Laid-open Patent Publication No. Hei 11-86893 discloses a fuel evaporator equipped with a combustion burner. In this fuel evaporator, fuel is burned with the combustion burner to generate heat, and a heat exchanger utilizes the resulting heat for raising the temperature of the raw material to evaporate the raw material.
Further, a warm-up apparatus equipped with a catalyst combustor is known. The catalyst combustor generates a gas for raising the temperature of the raw material. For example, a fuel evaporator disclosed in Japanese Patent Application No. Hei 11-315996 (unpublished) is provided with a catalyst evaporator. And the electric heater 101 shown in FIG. 4A and the combustion burner 201 shown in FIG. 4B are used for the purpose of immediately raising the temperature of the catalyst combustor.
However, when the flow rate of the exhaust gas (also referred to as an xe2x80x9coff gasxe2x80x9d) from the fuel cell becomes greater, electric power consumption becomes greater in the case of heating with the electric heater 101. Meanwhile, in the case of heating with the combustion burner 201, there are problems, such as increasing amount of the exhaust gas of the combustion burner 201 and increasing size of the burner itself.
However, because both of the above warm-up apparatuses are poor in heating efficiency, it takes time for completing the warming-up of the fuel evaporator 100 after actuating or starting the warm-up apparatus.
Further, heating with the combustion burner 201 is liable to burn the raw material at a relatively high temperature and thus to emit toxic substances, such as NOx (nitrogen oxides).
In order to eliminate the foregoing drawbacks of the prior art, the present invention seeks to provide a warm-up apparatus for a fuel evaporator with small and low electric power consumption, and having an actuation/warm-up system constitution allowing a quick and reliable warming-up operation, and ensuring clean gas emission.
According to the present invention, there is provided a warm-up apparatus for a fuel evaporator comprising:
a catalyst combustor for catalytically burning exhaust gas from a fuel cell to produce combustion gas and supplying said fuel evaporator which evaporates raw fuel liquid with the produced combustion gas as an evaporation heat source;
an exhaust gas passage for transferring exhaust gas to the catalyst combustor;
a combustion gas transferring device including a fuel injection portion and a combustion catalyst, and injecting fuel from said fuel injection portion onto said combustion catalyst, where the fuel is catalytically burned to produce combustion gas, and thereafter transferring the produced combustion gas to said catalyst combustor, wherein said combustion gas transferring device is positioned on one side of said exhaust gas passage.
With the above constitution of the warm-up apparatus, the following effects can be achieved.
(1) The combustion gas transferring device including a fuel injection portion and a combustion catalyst is positioned on one side of the exhaust gas passage, though which the exhaust gas is transferred to the catalyst combustor, and the combustion gas, which is produced by injecting fuel from the fuel injection portion to the combustion catalyst and thereafter catalytically burning the fuel, is transferred to the catalyst combustor. Therefore, it is possible to carry out low temperature combustion with little NOx emission, enabling the catalyst combustor to rise to the starting temperature while emitting clean exhaust gas to the outside.
(2) Because the combustion gas transferring device is positioned on one side of the exhaust gas passage and not in the same flow direction of the exhaust gas passage, the combustion catalyst of the combustion gas transferring device is hardly heated by radiation heat transfer from the catalyst combustor. Therefore, backfire toward the exhaust gas passage can be prevented in a reliable manner.
According to another aspect of the present invention, the combustion gas transferring device comprises a swirler generating a gaseous swirl flow with regard to the fuel injected.
Because the combustion gas transferring device comprises a swirler generating a gaseous swirl flow with regard to the fuel injected, fuel can be uniformly atomized and finely dispersed and a uniform fuel/air mixing ratio can be obtained. This results in stable composition of the combustion gas and uniform heat impartment to the following catalyst combustor.
According to another aspect of the present invention, the combustion gas transferring device includes a combustion gas outlet which opens from an upstream of a flow of the exhaust gas toward the catalyst combustor.
Because the combustion gas transferring device includes a combustion gas outlet which opens from an upstream of a flow of the exhaust gas toward the catalyst combustor, it is possible to effectively supply the combustion catalyst of the catalyst combustor with the combustion gas generated at the combustion gas transferring device.
It is preferable that the combustion gas outlet is provided at a position where the combustion catalyst of the combustion gas transferring device is not heated due to radiation heat transfer from a combustion catalyst of the catalyst combustor while the combustion catalyst of the catalyst combustor rises to high temperatures during the steady driving.
It is also preferable that the combustion gas transferring device comprises an injector as the fuel injection portion, an air injection nozzle, the combustion catalyst and a combustion gas outlet.
It is also preferable that the air injection nozzle is a swirler generating a gaseous swirl flow with regard to the fuel injected.
According to another aspect of the present invention, the exhaust gas passage is provided with a cover plate, which extends from a wall of the exhaust gas passage along a flow of the exhaust gas and partly blocks the flow of the exhaust gas.
With such an arrangement of the cover plate, the following effects can be achieved.
(1) Providing the cover plate prevents the flow of the exhaust gas from being drawn toward the combustion gas transferring device. Therefore, the exhaust gas does not burn due to contact with the combustion catalyst of the combustion gas transferring device.
(2) Because the cover plate extends from the wall of the exhaust gas passage along the flow of the exhaust gas, the cross-sectional area of the exhaust gas passage is substantially constant throughout the lengthwise direction. Therefore, pressure loss of the exhaust gas passage becomes smaller and a drift flow hardly occurs, leading to smooth flow of the exhaust gas toward the catalyst combustor.
Further, in comparison with the constitution without the cover plate, the combustion catalyst of the combustion gas transferring device is not subject to radiation heat transfer from the combustion catalyst of the catalyst combustor during the steady driving. For this reason, backfire due to the exhaust gas to be burned by the combustion catalyst of the combustion gas transferring device can be prevented in a more reliable manner.
It is preferable that the combustion catalyst of the combustion gas transferring device is based on, as a substrate, an expanded metal made of iron-chromium made stainless steel.
It is preferable that a fuel injection device is provided on one side of said exhaust gas passage.
It is also preferable that that the fuel injection device is capable of directly injecting fuel onto the combustion catalyst of the catalyst combustor when the combustion catalyst is thermally activated.
It is also preferable that the fuel injection device comprises an injector, an air injection nozzle, and a fuel outlet to the exhaust gas passage.
Further, it is preferable that the air injection nozzle is a swirler generating a gaseous swirl flow with regard to the fuel injected.
Further, it is also preferable that an inlet of the catalyst in the form of a layer is provided with a stainless steel made perforated plate for regulating a flow of the combustion gas while uniformly transferring the combustion gas from the combustion gas transferring device into the catalyst layer.